1. Field of the Invention
This invention relates to a method for accurately applying liquid samples in a biochemical analysis process, and a device for carrying out the method.
2. Description of the Prior Art
Qualitative or quantitative analysis of a specific chemical constituent in a liquid sample is generally conducted for various industrial purposes. Particularly, it is very important in biochemical and clinical fields to quantitatively analyze chemical constituents or physical constituents in body fluid such as blood or urine.
Recently, as disclosed in, for example, Japanese Patent Publication No. 53(1978)-21677 and Japanese Unexamined Patent Publication No. 55(1980)-164356, a dry type chemical analysis slide was developed for use in a system designed for performing quantitative analyses, with which system the amount of a specific chemical constituent or a specific physical constituent contained in a droplet of a liquid sample, which is simply applied to a slide, is determined. It is possible to analyze a liquid sample more simply and more accurately with methods in which a chemical analysis slide is used than with methods in which a conventional wet type analysis is carried out. Therefore, it is desirable to use chemical analysis slides, particularly in medical organizations, research laboratories, or the like where many samples must be analyzed.
In order to use a chemical analysis slide in the analysis of a chemical constituent or the like contained in a liquid sample, a measured amount of the liquid sample is put on the chemical analysis slide and is kept at a predetermined temperature (i.e. incubated) for a predetermined time in an incubator, which causes a color reaction. The chemical analysis slide is then exposed to light having a wavelength which is selected in advance, the selection of which wavelength depends on the constituents of the liquid sample and the constituents of a reagent contained in the reagent layer in the chemical analysis slide. Quantitative analysis of a chemical constituent or the like in a sample is carried out by irradiating a reaction product which forms on the chemical analysis slide with light and finding the ratio of transmitted vs. reflected light.
In medical organizations, research laboratories or the like where many liquid samples are analyzed, it is desirable to conduct analyses automatically and sequentially. To satisfy this need, various chemical analysis apparatuses have been proposed, which use the aforesaid chemical analysis slides. One such chemical analysis apparatus is disclosed in, for example, Japanese Unexamined Patent Publication No. 56(1981)-77746. Also, as a means with which liquid samples can be automatically and sequentially analyzed, an apparatus is proposed in, for example, U.S. Pat. No. 3,526,480, in which apparatus a long tape-like test film containing a reagent is used instead of the aforesaid chemical analysis slides, and the application, incubation and measurement of samples are carried out sequentially on adjacent portions of the test film. The operating cost of an apparatus using a long tape-like test film is lower than the operating cost of an apparatus using chemical analysis slides, and a simple mechanism makes it possible for measurements on many liquid samples to be carried out sequentially.
The chemical analysis slides and the long test film will hereinbelow be generically referred to as the test film. In biochemical analysis apparatuses having the configuration described above, a special device is employed with which liquid samples are applied to the test film. With the device for applying liquid samples, a liquid sample is accommodated in a sample applying nozzle and is delivered therefrom until a droplet of the liquid sample forms at the leading edge of the sample applying nozzle. The sample applying nozzle is then moved down until the droplet comes into contact with the test film. The droplet is thus applied to the test film with the aid of surface tension. The method for applying liquid samples, wherein a droplet of a liquid sample forms at the leading edge of a sample applying nozzle instead of being jetted out of the sample applying nozzle, is suitable for biochemical analysis processes wherein only very small amounts (for example, approximately 4 .mu.l) of the liquid samples are available.
In order to accurately to apply liquid samples to the test film with the aforesaid type of device for applying liquid samples, it is necessary that the distance between the leading edge of the sample applying nozzle and the surface of the test film, to which surface a liquid sample is to be applied, be always constant at the time of sample application. However, test films containing different reagents are used in accordance with the types of the constituents in the liquid samples which are to be subjected to measurement. The thickness of the test films often differs depending on the types of reagents contained in the test films. Therefore, if the position of the leading edge of the sample applying nozzle is constant during sample application, a sample application may not be carried out accurately depending on the type of test film used. Such problems occur in multi-channel type devices wherein a plurality of test films containing different reagents are accommodated, to which test films liquid samples are sequentially applied, and in single-channel type devices wherein a plurality of test films containing different reagents are sequentially used.
Also, in multi-channel type devices, the height at which each test film is supported fluctuates because of fluctuations in the dimensional accuracy of a plurality of supporting means which support the test films. In such cases, the distance between the sample applying nozzle and the surface of each test film, to which surface a liquid sample is to be applied, changes.